Без слов:
#dig microsoft.com MX
...
;; ANSWER SECTION:
microsoft.com. 3499 IN MX 10 mail.global.frontbridge.com.
...
#telnet mail.global.frontbridge.com. 25
Trying 207.46.51.86...
Connected to mail.global.frontbridge.com.
Escape character is '^]'.
220 mail190-sin.bigfish.com ESMTP Postfix EGGS and Butter